Consider 25 million users. Even if all 25 million were on the $9.99 plan, that would mean each user pays $119.88 a year, and you're talking a total annual revenue of $2,997,000,000. If everyone was on the $19.99 plan you're looking at annual revenues of $5,997,000,000.
Factor in the storage costs (which I'm sure they'll get a good rate for but don't have any data for) and a $10 billion valuation is simply ludicrous.
The numbers just don't stack up.